Resurrect net-p2p/microdc2 and unbreak the build: in the configure script,
libxml2 versions were compared algebraically (-ge), which made our current
version 280 appear smaller than checked-against 2616. It was fixed once,
by mezz@ in r225813, but not in a very good way (only for libxml 2.7).
While here, cleanup and stagify the port.